An inflator for inflating a vehicle occupant protection device, such as an air bag, contains a source of inflation fluid for inflating the air bag. In a particular type of inflator, the source of inflation fluid comprises a body of ignitable gas generating material. That type of inflator further includes an igniter. The igniter is actuated so as to ignite the gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired to protect an occupant of the vehicle. As the gas generating material burns, it generates a large volume of inflation gas which is directed to flow from the inflator into the air bag to inflate the air bag. When the air bag is inflated, it extends into the vehicle occupant compartment to help protect an occupant of the vehicle from a forceful impact with parts of the vehicle.
Such an inflator commonly has an elongated cylindrical housing. The housing is closed at one end by an end wall of the housing, and is closed at the other end by a closure cap. A tubular structure is contained in the housing. The tubular structure extends along the length of the housing between the closure cap and the end wall of the housing, and defines an elongated cylindrical combustion chamber in which the body of gas generating material is contained. The tubular structure also defines a filter which surrounds the combustion chamber. The filter cools and filters the gas as the gas flows radially outward through the filter from the combustion chamber toward the housing. A plurality of gas outlet openings extending through the housing direct the gas to flow radially outward from the inflator toward the air bag.
The body of gas generating material has approximately the same size and shape as the cylindrical combustion chamber. Accordingly, the body of gas generating material has an elongated cylindrical shape with longitudinally opposite ends adjacent to the opposite ends of the combustion chamber. Moreover, the elongated body of gas generating material is defined by a plurality of separate, shorter cylindrical grains of gas generating material. The grains of gas generating material are arranged concentrically in a row extending along the length of the combustion chamber.
The igniter is supported by the closure cap adjacent to one end of the combustion chamber. The igniter is thus located adjacent to the first few grains of gas generating material in the row of grains. As a result of this arrangement, ignition of the body of gas generating material begins at the first few grains of gas generating material in the row, and proceeds along the length of the body of gas generating material as all of the grains in the row are ignited successively.